EP-A-690,012 describes a barrier package for fresh meat products where the meat product is loaded onto a support member, such as a tray, and the package is then closed by applying an inner oxygen-permeable film over the product and the support member and an outer oxygen-impermeable film over the oxygen-permeable one. The two films are at least 0.25 μm apart, the space between them comprises an oxygen-permeable region and a minimum discrete free volume within the package is present to contain at least the amount of oxygen necessary to inhibit discoloration of the packaged meat product during its shelf-life. The teaching of EP-A-690,012 is that by keeping such a minimum gap between the two films the oxygen contained in the package will have access to the entire surface of the meat product, including the upper one where the inner oxygen permeable film is (or may come) in contact with the meat. Discoloration is thus prevented also when the packaged meat extends upwardly with respect to the height of the tray walls, which is the most critical situation in barrier packaging of fresh meat.
EP-A-690,012 illustrates various alternative packages where the combination of inner oxygen-permeable and outer oxygen-impermeable films complies with the claimed requirements. However in the detailed description it concentrates on the embodiments where the spacing between the two films, where oxygen may freely circulate, is obtained by means of a particulate composition present between the two films.
In a comparative example of EP-A-690,012, carried out in the absence of particulate, the thin oxygen permeable region between the two films was not maintained and meat discoloration was observed at top surface.
In another comparative example of EP-A-690,012, the process used to maintain the gap between the two lidding films, in the absence of particulate, led to a loose outer package and unacceptable pack appearance.
While the particulate used in EP-A-690,012 is said not to negatively affect the optics of the package, nonetheless it would be preferable to avoid the presence of such particulate for many reasons, e.g., improving the overall pack appearance, avoiding possible food contamination, increasing the number of alternative films and combinations thereof that could suitably be employed, etc.
The Applicant has therefore thoroughly investigated this packaging system and has discovered that it is possible to obtain a twin lidded package as claimed in EP-A-690,012, with an acceptable pack appearance, without the need of a particulate material between the two lidding films, by a lidding process where the two lidding films are superposed one to the other and wound together in a single supply roll and, before entering into the lidding station, are briefly separated and then again superposed one over the other, thus allowing a thin layer of gas to be trapped between the two. This film separation can be achieved very easily by means of one or more poles positioned in the packaging line after the lidding film unwinding station and before the lidding station.
The use of the lidding films in the form of a composite of two films, wound superposed in a single roll, besides allowing the use of conventional lidding machines with just a minor modification for the films temporary separation, has the great advantage of giving an exceptional pack appearance as no wrinkles or plies are created in the lidding process due to the fact that the two films are equally tensioned in the supply roll. This is achieved in the manufacture of the single supply roll by separately and continuously adjusting the tension of the single films while unwinding them from their respective rolls to compensate for the different elongations.
The brief separation between the two films before the lidding step allows the creation or reconstitution of a thin air layer between the two, where the air contained therein will then be freely exchanged through the oxygen-permeable food-contact lidding film with the oxygen that will be present within the end package. This will be sufficient to prevent meat discoloration even in those points (top surface) where the inner oxygen-permeable film is in contact with the meat product (or may come in contact with the meat product when the package is e.g. vertically displayed in the shelves or incorrectly handled in the distribution cycle) and the visual impression is that the outer oxygen-impermeable film, particularly if shrunk, is in its turn in contact with the oxygen-permeable inner film.
The Applicant has also found that particularly good results can be obtained using thin lidding films.
Particularly it has been found that the use of a thin food-contact gas-permeable film will guarantee a quick and easy oxygen-exchange between the thin oxygen-permeable region separating the two lidding films and the discrete free volume of the package containing the amount of oxygen required to prevent discoloration. This oxygen-exchange is necessary during the whole shelf-life of the package as oxygen is gradually absorbed by the meat and discoloration can therefore be prevented only if the amount of oxygen consumed in the thin layer close to the meat surface is continuously restored.
Also the oxygen-impermeable film needs not to be thick and it has been found that if its thickness is controlled, also the pack appearance is improved.
Furthermore it has been found that when according to a preferred embodiment of the invention the lidding films are heat-shrinkable, using thin films it is easier to avoid tray distortion that otherwise might occur with some of the conventional rigid or foamed trays on the market.
The Applicant has also found that a composite of thin lidding films suitable for use in this packaging system can conveniently be obtained by delaminating a suitably selected oxygen-barrier film into an oxygen-permeable portion and an oxygen-impermeable portion and then superposing said two components, in a sort of inverted position, to guarantee heat-sealability of the films and thus package hermeticity.
These findings are underlying the present invention.